1. Field of the Invention
The present invention generally relates to an image processing system, and especially relates to a suitable technology for an apparatus that rasterizes object information, stores, and transmits the information as a bit map image at a printing process, and an apparatus that determines an attribute, stores, and transmits the attribute as an attribute image at a copying process.
2. Description of the Related Art
Generally, a document drawn up by a computer is printed by a printer through the following processes.                (1) Document data are converted into two or more drawing commands.        (2) The drawing command is analyzed by software known either as a printer driver or a printer controller, and a raster image is generated.        (3) A printer output signal is generated through a color conversion process, a pseudo halftone process, and so on performed on the raster image.        (4) Perform printing.        
In order to output a high quality color image by the printer, a color process and a halftone process are required depending on the types of the images, such as a natural image, a graphic image, a line drawing (thin line), and a character. That is, if an image includes two or more of the image types, an optimal image process for each image type is needed.
For example, according to JPA 2000-11191, a document image described by a drawing instruction is developed (expanded) into a bit map image, and a code showing the image typed is included in a bit map image; thereby, the rastering process, wherein the image type is determined with sufficient precision, can be performed with a small capacity memory.
Here, there is a requirement to store the bit map image (also called an attribute image), to which the codes showing the image kinds are developed, with a still smaller storage space. For example, there is a method of storing the attribute information at a low resolution. According to JPA 8-98030, the attribute information for controlling UCR (undercolor removal) is compressed into one set of information per 4×4 pixels, and the compressed information is stored.
However, if resolution is lowered in an attempt to reduce the storage space, quality of the image is degraded. For example, when a character and a thin-line drawing are present on a graphic image, change of image processes for different attributes becomes noticeable at boundaries.